• Every major animal phylum that exists on Earth today, as well as a few more that have since become exnct, appeared within less than 10 million years during the early Cambrian evoluonary radiaon, also called the Cambrian explosion.

• Phylum Brachiopoda is represented by the brachiopods, marine animals that have calcareous or chino- phosphac shells, or valves, that surround a variety of internal organs and muscles. Brachiopod valves are hinged at the rear, while the front can be opened for feeding or closed for protecon. In a typical brachiopod a stalk-like pedicle projects from an opening called a foramen in the larger ventral valve, aaching the animal to the seabed but clear of silt that would obstruct the opening. • Brachiopods have an epithelial mantle that secretes and lines the shell, and encloses the internal organs. The brachiopod body occupies only about one-third of the internal space inside the shell, nearest the hinge. Like bryozoans, brachiopods have a lophophore, a coil of tentacles whose cilia create currents that enables them to filter food parcles out of the water. Unlike bryozoans, brachiopod lophophores are non-retractable and occupy up to two-thirds of the internal space, near the front where the valves gape when opened. • Some brachiopods have a calcareous brachidium that supports the lophophore. Terebratula

Spiriferina

Zeilleria • Two major groups of brachiopods are recognized, arculate and inarculate. Arculate brachiopods have toothed hinges and simple muscles for opening and closing the two valves, while inarculate brachiopods have untoothed hinges and a more complex system of muscles used to keep the valves aligned. • Brachiopods possess a bilateral symmetry across their dorsal and ventral valves, unlike the pelecypods which have bilateral symmetry between their two valves. • Brachiopods are arguably the most important group of fossil animals. They arose in the Early Cambrian and flourished during the Paleozoic Era. Their diversity was remarkable — over 12,000 fossil species are known — yet there are only about 350 species alive today. • Class Inarculata • Class Arculata • Order Lingulida • Order Orthida • Order Acrotreda • Order Strphomenida • Order Pentamerida • Order Rhynchonellida • Order Spiriferida • Order Terebratulida • Order Lingulida (E. Cam.-Rec.): The • Order Acrotreda (E. Cam-Rec.): The lingulids have biconvex shells that acrotreds have mostly circular are nearly all chino-phosphac. shells that are chino-phosphac or The pedicle emerges posteriorly calcareous. The pedicle emerges between the valves without a through a foramen in the ventral special foramen. Example is Lingula. valve. Example is Orbiculoidea.

Lingula Orbiculoidea • Class Inarculata • Class Arculata • Order Lingulida • Order Orthida • Order Acrotreda • Order Strphomenida • Order Pentamerida • Order Rhynchonellida • Order Spiriferida • Order Terebratulida • Order Orthida (E. Cam.-L. Perm.): The orthids have subcircular to semiellipcal, generally biconvex shells with straight hinge lines and radial ribs. The foramen notches the edge of both valves. Examples include Dinorthis (Ord.), Rhapidomella (Dev.), and Tropidoleptus (Dev.).

Dinorthis Rhapidomella Tropidoleptus • Order Strophomenida (E. Ord.-E. Jur.): The strophomenids have shells with one valve convex and the other flat or concave. The hinge lines are straight. Foramen are very minute or lacking. Examples include Rafinesquina (Ord.), Leptaena (Sil.), and Chonetes (Dev.).

Rafinesquina Leptaena Chonetes • Order Pentamerida (M. Cam.-L. Dev.): The pentamerids have heavy, generally smooth, strongly biconvex shells with short hinge lines. An internal spondylium, a spoon-shaped calcareous muscle support, is variably developed. Examples include Kirkidium (Sil.), Pentamerus (Sil.), and Stringocephalus (Dev.).

Kirkidium Pentamerus Stringocephalus • Order Rhynchonellida (M. Ord.-Rec.): The rhynchonellids have biconvex shells that usually have strong radial ribs and very short hinge lines. They have well- developed foramen. Examples include Rhynchotrema (Ord.), Rhynchotreta (Sil.), and Camarotoechia (Miss.). Rhynchotreta

Rhynchotrema Camarotoechia • Order Spiriferida (M. Ord.-L. Jur.): The spiriferids have shells that have either rounded, very short hinge lines or extended hinge lines. Foramen are always present and a spiral brachidium is usually well-developed. Examples include Atrypa (Dev.), Athyris (Dev.), and Mucrospirifer (Dev.).

Atrypa Athyris Mucrospirifer • Order Terebratulida (E. Dev.-Rec.): The terebratulids have shells with very short, rounded hinge lines. Foramen are present as are looped brachidia. Examples include Terebratula (Jur.), Oleneothyris (Pal.), and Calloria (Rec.).

Terebratula Oleneothyris Calloria • Phylum Mollusca includes seven classes of animals: • Amphineura • Pelecypoda • Gastropoda • Conularida • Pteropoda • Scaphopoda • Cephalopoda • Mollusca include marine, freshwater, and terrestrial animals. Most of them have an exoskeleton or a shell of some kind secreted by the mantle. They are all free-moving and swim, crawl, or burrow. The body consists of a head (except in the pelecypods), a foot, and a dorsal poron which includes the internal organs and is covered by the mantle. They have well- developed circulatory, digesve, excretory, and nervous systems. Respiraon is carried out by gills. • The phylum is pelecypod represented by over 60,000 living species and

many thousands of fossil gastropod ones, but only the pelecypods (bivalves), gastropods (snails), and the cephalopods (squids, nauloids, and ammonoids) have an

abundant fossil record. cephalopod • The pelecypods, also known as bivalves, are represented by clams, muscles, and oysters, among others. They are nearly all marine. They have a calcareous shell of two valves with bilateral symmetry between the valves. Valve growth begins at an inial point, a beak or umbo, and proceeds outward concentrically. • Pelecypod valves are lateral, or le and right. They are mirror images of each other, with the plane of symmetry between the valves. • Pelecypod valves are closed by muscles and opened by hinge ligaments when the muscles relax. Teeth along the hinge aid in arculaon. The shell is made up of several layers. The external layer is the periostracum, a thin, flexible, dark-colored layer composed of a protein called concholin. The periostracum protects an underlying calcareous layer which is composed of an outer prismac calcic layer and an inner porcellaneous or pearly aragonic layer made up of thin subparallel lamellae. Jacobs et al. (2008) • Locomoon in pelecypods is accomplished by a hatchet- shaped foot capable of burrowing. An incurrent or branchial siphon draws in water bringing food to the mouth and oxygen to the gills; an excurrent or anal siphon carries off the waste products and water that has passed over the gills. Eyes are present in some pelecypods such as the scallop Pecten. • Pelecypods occupy a wide range of habitats and are found in dal zones to water as deep as 17,000 feet. Some are free-swimming, like the scallop Pecten.

Grill and Zuschin (2001) • Pelecypods are found in the fossil record in the Cambrian, but they are quite rare unl the Late Cambrian. They rapidly diversified during the Ordovician and Silurian. Examples include Orthonota (Dev.), Pecten (Carb.), Ostrea (Tri.), and Mercenaria (Jur.), among many others. Representaves of many of these genera are alive today.

Orthonota Pecten Ostrea Mercenaria • The rudists were among many bizarre pelecypods that evolved during the Mesozoic Era. They arose during the Jurassic and became so diverse during the Cretaceous that they were major reef-building organisms. The rudists went exnct at the end of the Cretaceous. • The gastropods are represented by the snails, single-valved mollusks, and include marine, freshwater, and terrestrial forms.

• The general anatomy of gastropods is similar to that of pelecypods, but they differ from pelecypods in having a more or less disnctly marked head which usually bears tentacles, eyes, and ears and usually contains a large Terrestrial gastropod cerebral ganglion. Marine gastropods would have a gill in place of a lung. • Gastropods are both herbivorous and carnivorous. Their mouth contains a radula, a minutely toothed, filelike, chinous ribbon, which is typically used for scraping or cung food before the food enters the esophagus. Some gastropods use their radula to bore into other shelled animals, while others, such as cone snails, secrete toxins and use them as poisoned harpoons. • Many marine gastropods are burrowers and have a siphon that extends out from the mantle edge through a Siphon siphonal canal. A siphon enables the animal to draw water into their mantle cavity and over the gill. They use the siphon primarily to “taste” the water to detect prey from a distance. Gastropods with siphons tend to be either predators or scavengers. • The embryonic shell is called the protoconch. The shell grows as a gradually widening cone which is Posterior wound around an axial pillar, the columella, or around a central tubular cavity. Each coil is known as a whorl. The last whorl, in which the animal lives, is known as the body whorl; all of the other whorls together form the spire. The aperture varies in form and it may be closed by a calcareous or chinous plate, the operculum, aached to the posterior part of Anterior the foot. • Whether conical or saucer- shaped, gastropod shells are Sinistral Dextral usually coiled into a spiral which is either right-handed (dextral) or le-handed (sinistral). The coiling is the result of the more rapid growth of one side of the gastropod’s body, and as it is usually the le side which grows more rapidly than the right, the dextral coil is the more common type. • The shell is oriented by Sinistral Dextral holding it so that the apex (posterior end) is above and the aperture (anterior end) is below facing the observer.

• In a dextral shell, the aperture is on the right side; in a sinistral shell, the aperture is on the le side. These are two species in the genus Neptunea. • Gastropods exceed all classes of mollusks in variety and importance. There are more than 30,000 known species, of which more than 20,000 are recent. • The first gastropods were exclusively marine and have been found in rocks as old as Late Cambrian. Most of the gastropods of the Paleozoic Era belong to primive groups. Examples include Maclurites (Ord.), Bellerophon (Ord.-Tri.), Lophospira (Ord.-Carb.), and Loxonema (Ord.-Carb.).

Maclurites Bellerophon Lophospira

Loxonema • The number of marine gastropod families increased steadily from the Ordovician. The first terrestrial and freshwater snails are found in the Carboniferous and in the Jurassic, respecvely. The ancestors of many modern gastropods are found in Cenozoic rocks. Examples include Conus (Mio.), Cypraea (Plio.), Murex (Plio.), Busycon (Pleis.), and Turritella (Pleis.).

Murex

Conus Cypraea Busycon

Turritella culefish • The living cephalopods are represented by Subclass Belemnoidea, which includes the squid culefishes, squids, and octopi, and Subclass Nauloidea, which

includes two modern species of octopus nauloids, Naulus and Allonaulus.

nauloid • Cephalopods are bilaterally symmetric carnivorous marine animals that are nearly all free- swimming. • The circulatory, digesve, nervous, and respiratory systems of cephalopods are all very highly squid developed compared to those of the other Mollusca. They have a defined head with a pair of highly developed eyes. The anterior poron of the foot is modified into arms or tentacles which surround the mouth. The mouth has beaklike jaws with calcified ps, and a radula. Internal or external, straight or coiled, aragonic shells are secreted by the mantle. • The so parts of Naulus are contained in the Naulus outermost compartment, or living chamber, of a coiled shell. A tubular extension of the mantle, the siphon, connects this chamber with the earlier-formed unoccupied chambers through perforaons in the septa, which separate the chambers. • A hood, formed from the inner pair of tentacles, serves the same funcon as the operculum in gastropods when the animal withdraws into its shell. Chambers are filled with gas and are connected by the siphuncle, a calcareous wall surrounding the siphon. The lines formed by the intersecon of the septa with the shell are called sutures. • Representaves of three subclasses of cephalopods, Belemnoidea (also known as Coleoidea), Nauloidea, and Ammonoidea, are found in the fossil record from the Late Cambrian to the present day. • Belemnoids were abundant during the Jurassic and Cretaceous. An example of a fossil belemnoid is Belemnitella (Cret.). • Some 2,500 species of fossil nauloids are known from the Late Cambrian to the Recent. They reached their maximum diversity during the Silurian, declined aer the Devonian, and nearly went exnct aer the Permian, the Triassic, and the Miocene.

• Nauloids may be disnguished from ammonoids by the posion of the siphuncle near the center of the septa.

• The nauloids have the simplest suture paerns of the chambered cephalopods. • Fossil nauloids may have straight, slightly curved, loosely coiled, or ghtly coiled shells. Examples include Orthoceras (M. Ord.), Cyrtoceras (Mid. Ord-M. Dev.), Gyroceras (Sil.-Dev.), Cenoceras (E. Jur.), and Naulus (E. Jur.-Rec.).

Orthoceras Cyrtoceras

Gyroceras Cenoceras • Some 7,500 species of fossil ammonoids are known from the Late Silurian to the end of the Cretaceous, when they went exnct.

• Ammonoids may be disnguished from nauloids by the posion of the siphuncle near the extreme ventral edge of the septa.

• Ammonoids may be classified into three orders, Goniada, Cerada, and Ammonida, based on how complex their suture paerns are. • Ammonoids may have straight, loosely coiled, or ghtly coiled shells. Examples include Bactrites (E. Dev.-L. Perm.), Mimoceras (E. Dev.), and Agoniates (M. Dev.).

Bactrites Agoniates • Ammonoids may be classified into three orders, Goniada, Cerada, and Ammonida, based on how complex their suture paerns are. • Three major types of suture paerns are found in the Ammonoidea: • Goniac: numerous undivided lobes and saddles; typically 8 lobes around the conch. This paern is characterisc of the Paleozoic ammonoids. • Cerac: lobes have subdivided ps, giving them a saw-toothed appearance, and rounded undivided saddles. This suture paern is characterisc of Triassic ammonoids and appears again in the Cretaceous “pseudocerates.” • Ammonic: lobes and saddles are much subdivided (fluted); subdivisions are usually rounded instead of saw-toothed. Ammonoids of this type are the most important species from a biostragraphical point of view. This suture type is characterisc of Jurassic and Cretaceous ammonoids, but extends back all the way to the Permian. • Goniates have the simplest suture paern of the ammonoids. They are found in the fossil record from the Middle Devonian to the Late Permian. Examples include Tornoceras (M. Dev.), Moncoceras (L. Dev.), and Gastrioceras (Penn.).

Tornoceras Moncoceras Gastrioceras • Cerates have a more complicated suture paern than the goniates. They are found in the fossil record from the Permian to the Triassic. An example is Cerates (M. Tri.).

Cerates • Ammonites have the most complicated suture paern of the ammonoids. They are found in the fossil record from the Early Jurassic to the Late Cretaceous. Examples include Phylloceras (E. Cret. ), Cletoniceras (Cret.), and Sphenodiscus (L. Cret.).

Phylloceras Cletoniceras Sphenodiscus